A traveling worker hears a unique ringtone on his cell phone, checks the screen and finds a presence notification that a colleague is awaiting a plane in the same airport. 

A ‘soccer parents’ presence channel’ on a dad’s SIP softphone shows all the team’s parents are available to share a group voice or IM session right now. 

A teenager who just wrecked his mom’s car checks the family presence channel on his mobile phone to find out his mother’s current mood.

These examples only hint at how presence technologies will enable a large class of services not achievable on existing mobile networks. 

Presence technologies already have revolutionized how and when network-connected ‘buddies’ communicate. A quick look at the instant messaging (IM) window on a PC tells which buddies are present and available to converse and which ones have stepped out or are otherwise engaged. In short, the availability of presence information puts the “instant” in instant messaging. Presence enables one to avoid the uncertain, delayed responses associated with ‘non-instant’ email or voice messages. The IP network user wastes less time and effort—not to mention network capacity—on attempts to communicate with absent interlocutors. 

Thankfully, presence technology and its benefits are not limited to IM. Through standard-setting work by the Internet Engineering Task Force (IETF), presence has largely worked its way into voice over IP (VoIP) through extensions of the Session Initiation Protocol (SIP), which has become the global standard for VoIP call set-up and tear-down. This work has been adopted as a core technology by the 3rd Generation Partnership Project (3GPP), a consortium of wireless standards bodies defining the evolution of the GSM technologies. 

As a result, mobile network users will gain instant knowledge of who is available, what they’re doing and even their mood at the present time. Further, this standards work will bring presence into the realm of wireless/wireline convergence, in effect affording anytime access to personalized applications and information over any network, via any device. In short, presence will help advance the definition of “mobility” in terms of people, rather than any single device. 

The SIP Connection

SIP provides a key nexus of cooperation between the 3GPP and the IETF. Wherever it can, the 3GPP is leveraging the IETF’s SIP standards in setting 3G wireless VoIP standards. In particular, 3GPP’s IP Multimedia. 3GPP also seeks to leverage work being produced by the IETF’s SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE) Working Group, which is building on SIP, to make VoIP and other wireless IP applications presence- and instant-communications-enabled. 

The SIP and SIPPING working groups are currently building extensions to SIP to better ensure the identity of a mobile user. This work extends the traditional concept of a certificate that is issued by a trusted party once, and for a long period of time, to having that third party assure a single message, or issue a certificate that is valid for a very short time. This addresses many of the issues that have made traditional Public-Key-Infrastructure (PKI) deployment difficult, and greatly simplifies the task of providing a secure identity statement for users on endpoints that frequently change where they are connected to the Internet. This secure identity will provide a trustable “Caller-ID” feature and help battle against IM and Voice spam.

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